Tuning devices for broadcast radio receivers

The wide choice of entertainment provided by the broadcast receiver is perhaps its most important feature, and the development of tuning devices to simplify the exercise of that choice has played an outstanding part in radio receiver design. Both station selection and ready identification of a programme found by random searching are involved. The paper opens with a brief historical review of tuning-device evolution from the introduction of single-knob tuning to the immediate pre-war designs. Listening tests are used to establish the degree of mistuning to cause observable deterioration of quality, and to suggest a target design tolerance for tuning errors. A consideration of frequency stability on the broadcast bands leads to an analysis of design limitations and establishes pre-set tuning on medium and long waves and band-spread tuning on short waves as important problems. The design of pre-set tuning devices is reviewed, together with their power drive and remote control, and the development of band-spread tuning is described, together with the associated receiver circuits. Appendices give the measured frequency response and harmonic-content characteristics of the receiver used in the listening tests, together with a mathematical analysis of these characteristics as derived from the intermediate-frequency response.